1. Field of the Invention
The present invention relates generally to a liquid crystal display device and more particularly to a liquid crystal display device having a transflective color filter on an array (COA) structure.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device includes a liquid crystal display panel, a backlight unit, a driving unit, a chassis and the like. The LCD panel is composed of a thin film transistor (TFT) substrate having a TFT formed thereon, a color filter substrate bonded to the TFT substrate and having a color filter layer formed thereon, and a liquid crystal layer disposed between the two substrates.
During the manufacturing of a LCD panel, the TFT substrate and the color filter substrate are bonded to each other. During this bonding process, a precise alignment of the two substrates is required. Problematically, even a minute misalignment of the substrates produces a defect in the LCD panel and specifically, in a reduction in the LCD panel's opening rate. In order to solve these problems, a color filter on array (COA) structure has been developed wherein both the TFT and the color filter are formed on the same substrate. More specifically, a TFT is formed on a TFT insulating substrate and a color filter layer is formed on the TFT to prepare a first substrate, and an opposing second substrate is prepared by forming only a common electrode on a second insulating substrate. The COA structure eliminates the need for precise alignment between the TFTs and the color filters upon bonding, thus advantageously reducing alignment errors upon bonding the substrates.
An LCD panel is a non-light emitting element and thus a backlight unit for supplying light is disposed on the rear side of the TFT substrate. The light radiated from the backlight unit changes its light transmissivity with arrangement of the liquid crystal layer.
An LCD device is categorized into a transmissive LCD device that uses only the light supplied from a backlight unit and a transflective LCD device that uses external light in addition to light from a backlight unit.
The transflective LCD device simultaneously uses light from a backlight unit that is transmitted through a transmissive area and external light from a source outside the device itself (such as the sunlight or ambient light). Thus, in outdoor or daytime environment where there is an abundance of ambient light, light incident on the LCD panel can be used by being reflected off a reflective film in a reflective area of the display that is formed on a TFT substrate. This ability to take advantage of ambient light reduces power consumption to one third of that used by a comparable transmissive LCD device. Thus, the service life of the light source and the battery can be extended by operating an LCD device in a transflective mode. A longer battery life improves the general performance of portable communication devices that incorporate the LCD.
For these reasons, LCD devices having a transflective COA structure have become increasingly popular. A transflective COA structure combines the low power consumption advantage of a transflective LCD panel and the low defect rate of the COA structure. However, in the current transflective COA structure, a difference in the light path through the color filter layer occurs between the transmissive area and the reflective area, thus causing a difference in the lengths of light paths between the transmissive and reflective areas. This difference in the light path lengths create inconsistencies in the reproduced colors, thereby decreasing color reproductivity. In order to achieve consistency in color and enhance color reproductivity, a light hole is formed on the color filter layer in the reflective area. Lights passing through the color filter layer and the light hole of the reflective area are mixed to match the color produced in the transmissive area, enhancing color reproductivity.
However, when forming the light hole, a stepped portion forms in the hole area during patterning. The presence of the stepped portion causes unintended orientations of the liquid crystal in the reflective area and defective driving of the liquid crystal by creating a difference in the cell gap among the hole area, the reflective area and the transmissive area.